Step 1

Preheat the oven to 350º fahrenheit

Step 2

Spread the bread cubes on a baking sheet and bake for 15 minutes, until very lightly browned

Step 3

Set aside.Heat the oil and butter in a large sauté pan over medium heat

Step 4

Add the pancetta and cook for 5 minutes, until starting to brown

Step 5

Stir in the leeks and onion and cook over medium heat for 8 to 10 minutes, until the leeks are tender and onion is translucent

Step 6

Stir in the mushrooms, tarragon, sherry, salt and pepper, cook for 10 to 12 minutes, until most of the liquid evaporates, stirring occasionally

Step 7

Remove from heat and stir in the parsley.In a large mixing bowl, whisk together the eggs, cream, chicken stock and 1 cup of the Gruyere

Step 8

Add the bread cubes and mushroom mixture, stirring well to combine

Step 9

Set aside at room temperature for 30 minutes to allow the bread to absorb the liquid

Step 10

Stir well and pour into a 2 ½-to-3-quart gratin dish (13 x 9 x 2 inches)

Step 11

Sprinkle with the remaining ½ cup Gruyere and bake for 40 to 45 minutes, until the top is browned and the custard is set

Step 12

Serve hot.Adapted from Barefoot Contessa Foolproof by Ina Garten